Some portions continued in use after abandonment. It seems fairly obvious the el's in Manhattan were doomed; but they remain in service in the outer boroughs. My personal favorite was the Third Avenue El in the Bronx. Wish that would have survived.

The Bronx Third Avenue el and the Myrtle Avenue line left significant gaps in coverage when closed. Unfortunately no one could foresee that those neighborhoods would have revivals decades later.

If the Brooklyn-Queens light rail is built a branch from the Navy Yard to Bushwick and maybe beyond (via Park Avenue or Myrtle Avenue) would be a plausible extension. The distance from Kent Avenue to Broadway is perhaps a mile or so?

I guess Staten Island is too "low brow" for "untapped;" any discussion of "lost NYC rail lines" should include Staten Island's SIRT North Shore Line and SIRT South Beach Branch Line, both of which lost passenger service in 1953. While the South Beach Branch is hopeless (the right of way no longer exists), the North Shore Line would be extremely useful for north shore residents who today have to tolerate the oxymoron called "bus service."

There's a post on LIRR that the last ferry from 34th St. to Long Island City operated on March 3, 1925. How long after that did the 34th St. branch of the El last? And did it connect with the 3rd Ave. as well as 2nd? Through from South Ferry, or shuttle from somewhere closer?

Definitely, it would have served Brooklyn well if the Myrtle Avenue el had stayed in service as far as Jay Street. I do wonder though whythe abandoned trackways at Myrtle -Broadway continue as far as they do beeyond what's needed to hold up the control towers.